1. Field of the Invention
This invention relates in general to a device and method for removing plasma from a flexible bag containing a layer of plasma over a layer of red bood cells.
2. Description of the Prior Art
Blood plasma is used to manufacture a number of medical products. In donation centers, the whole blood is collected conventionally in a flexible clear bag. Then while the donor waits, the bag of whole blood is placed in a centrifuge. The blood will separate into two layers, with a plasma layer above the red blood cell layer. The plasma is fairly clear and makes up about sixty percent of the whole blood.
The operator then places the segregated bag into an extractor device. The extractor device has a fixed plate and a spring loaded movable plate, with the bag being supported vertically between them. The bag is squeezed between the plates by spring force, with the plasma being forced out the top through a tube and into a collection bag. Once substantially all of the plasma is forced out, the spring pressure is released. The red blood cells are then fed back into the donor. Returning the red blood cells to the donor allows the donor to donate twice per week. If the red blood cell portion cannot be returned, the donor must wait eight weeks before donating again.
During the extraction process, the operator observes the bag and releases the pressure when he sees that the plasma has nearly all flowed from the bag. The process of forcing the fluid from the bag takes about three to seven minutes, and one operator may have several bags being extracted at the same time, as well as controlling the centrifuge. Consequently, the operator may inadvertently allow some of the red blood cells to escape into the bag collecting the plasma by failing to release the spring pressure at the proper time. If contamination occurs, the contaminated plasma must be centrifuged again to separate the red blood cells. The recentrifuged plasma is again placed in an extractor device and forced out of the bag. During this second operation, some of the plasma cannot be squeezed from the bag, and will be lost.
Also, a contamination error is a hazard to the donor. Red cells are oxygen carriers and have a short life at room temperatures. The red blood cells that inadvertently were allowed to flow into the plasma collecting bag will be lost. They cannot be returned to the donor after recentrifuging because due to the time loss they will probably be dead. If a large amount of red blood cells are lost, the donor will be unable to return for eight weeks. Consequently, not only does a contamination error result in additional time being spent by the operator in recentrifuging the collected plasma, but it also results in a loss of expensive plasma and may cause donor disqualification.